Feline Retroviruses Flashcards
Which feline viruses are classed as retroviruses?
- Feline leukaemia virus (FeLV)
- Feline Immunodeficiency virus (FIV)
- Feline syncytium-forming virus (FeSFV)
Classification of a virus is based on which factors?
- The genome: RNA or DNA
- Number and sense of RNA/DNA strands
- Morphology
- Genome sequence similarity
- Ecology
What is the genome of Retroviridae?
RNA
What are the main characteristics that only this virus classification has?
- Truly diploid
- Genome is produced by cellular transcriptional machinery
- Genome requires a specific cellular RNA for replication
Describe the main structural features of a virus
- Outer glycoproteins for attachment
- Viral envelope
- Inner capsid
- Core of reverse transcriptase and 2 identical RNA strands
What is reverse transcriptase?
Virally encoded RNA dependent DNA polymerase
How does reverse transcriptase work?
Uses the viral RNA genome as a template for the synthesis of complementary DNA copy
The virus need RT as it is not found in the host
What is the role of integrase?
Bind the viral cDNA generated by RT and the host DNA which allows insertion of the viral genome into the hosts DNA, when the host makes copies of its DNA it is also copying the viral DNA
Which subtype of Feline leukaemia virus is transmissible?
type A
How can a host have type B or C FeLV if only type A is transmissible?
B and C are recombinants or mutants of A so are only found with type A and need type A for replication
Name the 4 syndromes caused by FeLV
RAIN
- Reproductive failure
- Anaemia
- Immunodeficiency
- Neoplasia (tumours)
What are the routes of infection for FeLV?
- excreted in saliva, urine, faeces and milk
- requires close FRIENDLY contact
- passed to offspring
Describe the pathogenesis of FeLV
- Replicates in oropharynx and local lymph nodes: primary viraemia: antibody negative, virus positive
- Continues to replicate in lymph and bone marrow: secondary viraemia
- Persistent latent infection: virus negative, antibody positive
- An ineffective immune response leads to clinical disease and death
How does age affect susceptibility to FeLV?
Susceptibility to persistent infection decreases with age
What are the 4 main types of lymphoma associated with neoplasia/FeLV?
- Mediastinal (thymic)
- Multicentric
- Alimentary
- Leukaemic
Describe mediastinal lymphoma
- in younger cats
- thymus and local lymph nodes
- dyspnoea, weight loss, regurgitation
- muffled heart sounds
- pleural fluid containing neoplastic lymphocytes
Which type of lymphoma can affect any organ/tissue?
Multicentric
Where is the main site affected by alimentary lymphoma?
Duodenum/colon - causes abdominal masses
Describe leukaemia
- Based in bone marrow, affect RBC production
- Raised WBCs, anaemia
- Pyrexia, weakness, anorexia
Compare primary and secondary FeLV associated anaemia
Primary: - RBC aplasia - total marrow aplasia - non-regenerative Secondary: - Regenerative - due to myeloid tumours in bone marrow
FeLV associated non-regenerative anaemia is associated with which subtype?
Subtype C
How does FeLV affect pregnancy/kittens
- Common cause of reproductive failure, reabsorption of foetuses at 3-5 weeks
- If survive to birth kittens are persistently infected: fading kitten syndrome
How can FeLV be controlled?
- Test and remove (rehome or euthanase)
- Test all cats in a colony and house separately all +ve
- Retest 12 weeks later: only double +ve need to be continually separately housed
- Reduce friendly contact: separate food bowls
When are kittens vaccinated for FeLV?
- At 8-9 weeks and again 3 weeks later
- If kittens are protected by MDA until 4 weeks they wont be protected by the vaccine until 13 weeks
Describe the epidemiology of FIV
- More common in males
- Most infected cats are >5 years old
- More common in free-roaming and feral cats in unstable colonies
How is FIV transmistted?
By biting - lots of virus in salvia
Through fighting/unfriendly contact
Describe the pathogenesis of FIV
- Virus infects lymphocytes, macrophages etc
- Within a week of inoculation get viraemia, then levels decrease
- Decreases CD4 T-cells (CD4:CD8 ratios)
- Decreased expression of MCHII
- cats can remain clinically healthy for years/life
How can FIV be prevented/controlled?
- no vaccine
- prevent cats fighting
- isolate infected cats
What are the 2 ways to diagnose any infection?
- Detect the microorganism
- Detect the immune response
Out of FeLV and FIV which test looks for an antigen and which looks for an antibody?
FeLV = antigen FIV = antibody
What are the tests to diagnose FeLV?
- Testing for bits of the virus: p27 antigen (present in infected cats) capture ELISA, immunofluorescence, isolation, PCR
- Antibody test
What are the tests to diagnose FIV?
- Bits of virus: isolation PCR
- Antibody: ELISA, immunofluorescence, western blot
What is sensitivity?
Proportion of true positives picked up by the test
What is specificity?
Proportion of true negatives picked up by the test
What are the positive and negative predictive values?
PPV = proportion of true positive results NPV = proportion of true negative results
